(1) Field of the Invention
The present invention relates to the Macaca mulatta (rhesus monkey) Nur77 (rhNur77) nuclear receptor and the nucleic acid encoding the rhNur77 nuclear receptor. The present invention further relates to methods for identifying analytes that modulate expression or activity of Nur77. Analytes that affect Nur77 expression or activity may be useful for treating or inhibiting inflammatory diseases such as osteoarthritis and various bone, neurological, and prostrate disorders. The rhNur77 may also be useful in treatments for particular cancers such as lung cancer, prostrate cancer, colon cancer, ovarian cancer, or gastric cancer.
(2) Description of Related Art
Nur77 is a transcription factor that belongs to the superfamily of nuclear receptors, which includes receptors for various steroid hormones, retinoids, thyroid hormone, and estradiol. The superfamily further includes a large group of receptors classified as orphan receptors because their natural ligands are not yet known. Nur77 is currently classified as an orphan receptor and has been variously known as HMR, N10, TR3, NP10, GFRP1, NAK-1, NGFIB, or MGC9485. Nur77 is expressed in various peripheral tissues and in some regions of the brain and has been implicated to have a role in cell proliferation, differentiation, and apoptosis.
Nur77 exhibits a close structural relationship to the orphan receptors Nurr1 (Hazel et al., Proc. Natl. Acad. Sci. USA. 85: 8444-8448 (1988); Milbrant, Neuron 1: 183-188 (1998); Ryseck et al., EMBO J. 8: 3327-3335 (1989); Nakai et al., Mol. Endocrinol. 4: 1438-1443 (1990)) and NOR-1 (Ohkura et al., Biochem. Biophys. Res. Comm. 205: 1959-1965 (1994); Maruyama et al., Cancer Lett. 96:117-122 (1995); Hedvat and Irving, Mol. Endocrinol. 9: 1692-1700 (1995)). All three of these orphan nuclear receptors comprise the Nurr subfamily of nuclear receptors which has been characterized as being able to bind to the same cis-acting consensus nucleotide sequence—the NGFI-B response element (NBRE)—to regulate target gene expression (Ohkura et al., Biochem. Biophys. Res. Comm. 205: 1959-1965 (1994); Wilson et al., Science 252: 1296-1300 (1991); Wilson et al., Mol. Cell Biol. 13: 5794-5804 (1993); Murphy et al., Gene Express. 5: 169-179 (1995)). For example, Nurr1 and Nur77 regulate expression of the Corticotropin Releasing Hormone (CRH) and proopiomelanocortin (POMC) genes by interacting with specific cis-acting sequences in their proximal promoter region.
Like most nuclear receptors of the nuclear receptor superfamily, Nur77 consists of an amino-terminal transactivation function 1 (AF1) near the amino terminus, which enables ligand-independent transcription activation; a core DNA binding domain (DBD) located near the center of the protein, which contains two highly conserved zinc finger motifs and which binds to specific nucleotide sequences; a hinge region, which permits protein flexibility to allow for simultaneous receptor dimerization and DNA binding; a conserved ligand binding domain (LBD) near the carboxy terminus, which includes a dimerization interface; and, a carboxyl-terminal activation function 2 (AF2) near the carboxy terminus, which enables ligand-independent transcription activation. Many nuclear receptors act as dimers, either as homodimers or as heterodimers. The dimerization interface in the LBD, the I-box, has been mapped to a region in the carboxyl terminal part of the LBD that corresponds to helix 10 in the canonical nuclear receptor LBD structure (Perlmann et al., Mol. Endocrinol. 10: 958-966 (1996); Lee et al. Mol. Endocrinol. 12: 325-332 (1998)).
Unlike most nuclear receptors, the Nurr subfamily of nuclear receptors are encoded by immediate early genes whose expression can be differentially induced in response to a variety of extracellular stimuli such as growth factors (Hazel et al., ibid.; Milbrandt, ibid.), neurotransmitters (Watson and Milbrandt, Mol. Cell. Biol. 9: 4213-4219 (1989)), and polypeptide hormones (Wilson et al., Mol. Cell. Biol. 13: 861-868 (1993); Murphy and Conneely, ibid.; Davis and Lau, Mol. Cell Biol. 14: 3469-3483 (1994)). Nurr1 and Nur77 are rapidly induced by CRH in primary pituitary cells, resulting in increased synthesis of POMC (Murphy and Conneely, ibid.). Glucocorticoid repression of the POMC gene is mediated by glucocorticoid receptor dependent inhibition of activation of the POMC gene by Nurr1 and Nur77 (Evans, ibid.; Philips et al., Mol. Cell. Biol. 17: 5952-5959 (1997)) and appears to antagonize negative feedback of ACTH synthesis and secretion by glucocorticoid in pituitary corticotrope cells (Okabe et al., J. Endocrinol. 156: 169-175 (1998). Because NOR-1 possesses an identical DNA binding domain and is capable of binding the same cis-acting consensus sequence as Nurr1 and Nur77, it has been included in the Nurr subfamily. Therefore, the close structural relationship, the identical cis-acting consensus sequence, and the ability of the different members of the Nurr subfamily of transcription factors to functionally complement one another are strong indications that the Nurr subfamily members might have redundancy of function.
Nur77 forms heterodimers with retinoid X receptor (RXR) (Perlmann and Jansson, Genes Dev. 9: 769-782 (1995); Forman et al. (1995); Zetterstrom et al., Science 276: 248-250 (1996)). The unique ability of the Nur77/RXR heterodimer complex to transduce RXR signals establishes a novel response pathway. Heterodimer formation may impart allosteric changes upon the LBD of the Nur77. These allosteric changes may confer transcriptional activities onto the Nur77-RXR heterodimer that are distinct from those of the Nur77 or RXR monomers. This would permit a limited number of regulatory proteins to generate a diverse set of transcriptional responses to multiple hormonal signals.
Nur77 appears to have a role in both apoptosis and cell proliferation. Kolluri et al. (Molec. Cell. Biol. 23: 8651-8667 (2003)), and Wilson et al. (Cancer Res. 63: 5401-5407 (2003)) have shown that Nur77 can induce apoptosis or cellular differentiation in the same cells depending on the stimuli and its cellular location. Cao et al. (Molec. Cell. Biol. 24: 9705-9725 (2004) has shown that RXR regulates Nur77/thyroid hormone receptor 3-dependent apoptosis by modulating its nuclear export and translocation to the mitochondria where it induces apoptosis. Other researchers have shown that parathyroid hormone can regulate Nur77 expression in bone (Tetradis et al., in Biochem. Biophys. Res. Comm. 281: 913-916 (2001)) and LH can regulate Nur77 expression in testicular Leydig cells (Song et al., Endocrinol. 142: 5116-5123 (2001). Promyelocytic leukemia protein PML is a tumor and growth suppresser that inhibits Nur77-mediated transcription by interacting with the DNA-binding domain of Nur77, which prevents it from binding its target promoter (Wu et al., oncogene 21: 3925-3933 (2002). The role of Nur77 in signal transduction has been discussed by Winoto and Littman, Cell 109: S57-S66 (2002).